The entire disclosure of Japanese Patent Application No. 2010-273264, filed Dec. 8, 2010, is expressly incorporated by reference herein.
1. Technical Field
The present invention relates to a wavelength-variable interference filter, an optical module equipped with the wavelength-variable interference filter, and an optical analysis device equipped with the optical module.
2. Related Art
In the past, there has been known an optical filter (a wavelength-variable interference filter) having mirrors disposed in an opposite manner on the respective surfaces of a pair of substrates, the surfaces being opposite to each other. See Japanese patent publication number JP-A-2010-204457. In such a wavelength-variable interference filter, multiple interference is caused in the incident light between the pair of mirrors. And then the light with a specific wavelength reinforced each other by the multiple interference is transmitted therethrough.
In the wavelength-variable interference filter of the above Japanese patent publication, a first substrate and a second substrate are disposed so as to be opposite to each other. Further, on the surface of the first substrate not opposite to the second substrate, a groove section having an annular shape is formed. And by forming the groove section, a columnar movable section is formed at the central part of the first substrate; and a diaphragm is formed to have an annular shape coaxial with the movable section. Further, between the pair of substrates, ring-like electrodes are provided respectively on the surface of the diaphragm, the surface being opposite to the second substrate, and on the second substrate so as to be opposite to each other; and further, mirrors are provided respectively on a surface of the movable section, the surface being opposite to the second substrate, and on the second substrate so as to be opposite to each other.
According to such a configuration, by applying voltages to electrode wires respectively extending from the pair of electrodes to the outer circumferential edges of the substrates, an electrostatic attractive force is generated between the pair of electrodes. The diaphragm is bent due to the electrostatic force to thereby displace the movable section provided with the mirror in the substrate thickness direction. And thus, it becomes possible to vary a gap between the pair of mirrors. Therefore, it becomes possible for the wavelength-variable interference filter to transmit the light with the specific wavelength corresponding to the gap.
In the wavelength-variable interference filter of the above Japanese patent publication, in the first substrate, the surface of the diaphragm opposite to the second substrate is provided with the electrode wire extending from the electrode to the outer circumferential edge of the substrate. Since the just one electrode wire is provided to the first substrate, the film stress of the electrode wire is applied only to a part provided with the electrode wire out of the diaphragm. Therefore, there is a possibility that the stress balance of the diaphragm becomes uneven to thereby cause deflection of the diaphragm. Thus, there is a possibility that the movable section of the first substrate is tilted, and the pair of mirrors fails to be parallel to each other.
Therefore, in order for improving the stress balance of the diaphragm in the first substrate, it is possible to form an electrode wire (an anti-deflection electrode wire) having the same configuration at a position symmetrical to the electrode wire described above taking the center point of the substrate as the center point of symmetry.
However, in some cases, there is no choice but to dispose the electrode wire at a position of the second substrate, the position being opposite to the anti-deflection electrode wire, due to the structural restriction such as the wiring condition of a module for incorporating the wavelength-variable interference filter. In such cases, since the electrostatic attractive force is generated between the anti-deflection electrode wire and the electrode wire of the second substrate, there is a possibility that the pair of mirrors fails to be parallel to each other. Thus, there arises a problem that it is not achievable to accurately set the gap between the pair of mirrors to a desired amount of gap.